The conventional pallet is made entirely of hardwood. The conventional pallet comprises bearers, aligned parallel to each other and connected to each other by two linear arrays of cross-planks or slats. Each slat of one of the linear arrays is nailed, at each end, to the upper surface of a respective one of the bearers. Each slat of the other linear array is nailed, at each end, to the bottom face of a respective bearer. Usually, each slat is also nailed to a central bearer which is located between the main bearers. Hardwood has to be used for the cross-planks (slats) and bearers of such pallets, even though it is considerably more expensive than softwood timber such as pine, because nails are used to assemble the pallet.
In addition to the cost factor in the manufacture of a wooden pallet (which is partly related to the increasing difficulty in obtaining suitable hardwood), the conventional wooden pallet has a number of disadvantages. The disadvantages include:
(a) the fact that the pallets are easily damaged by careless handling by the operators of fork-lifts, particularly (i) when the tynes of the fork-lift strike an end slat and dislodge it from its associated nails, and hence from the bearers, and (ii) when a fork-lift tyne is pushed into the end grain of a bearer during movement of the pallet by the fork-lift prior to the lifting of the pallet by the fork-lift, thus splitting the timber of the bearer; PA0 (b) the fact that when (as often happens) a pallet is dropped from a truck or loading dock and lands on a corner, the pallet is distorted diagonally; PA0 (c) the possibility of damage being caused to goods on the pallet which have been bagged or packed in cartons, by any nails protruding from the pallet; PA0 (d) the inherent weakening of the timber slats when nails are driven through the ends of the slats - often causing the wood of the slat to split; and PA0 (e) a badly damaged pallet is a complete waste of a timber resource, for a badly damaged pallet cannot readily be used as low-cost firewood in view of the expense incurred in the labour-intensive task of removing the nails to make the timber suitable for firewood. PA0 (a) each bearer is a hollow metal member of rectangular cross section, having an upper wall, a lower wall, an inner wall and an outer wall; PA0 (b) each bearer has an upper and a lower linear array of openings formed in the corners of the bearer at (i) the junction of the upper wall and the inner wall and (ii) the junction of the lower wall and the inner wall, each of said openings having a width such that it receives one end of one of said slats or planks; PA0 (c) each slat or plank has a pair of slots formed in one face thereof, each slot extending at right angles to the elongate direction of the slat or plank and having a thickness substantially equal to the thickness of the inner wall of a bearer, each slot being a distance from a respective end of its slat or plank which is equal to or less than the distance between the faces within a bearer of its inner and outer walls; and PA0 (d) the vertical distance between the level of the inside face of the upper wall and the level of the lowermost horizontal edge of an opening in the upper corner of a bearer is equal to the vertical distance between the level of the inside face of the lower wall and level of the uppermost horizontal edge of an opening in the lower corner of a bearer, which is slightly less than the distance between the bottom of a slot in a slat or plank and the face of such slat or plank in which a slot is not formed.
It has long been recognised that it would be advantageous if a nail-free pallet could be provided in place of the conventional wooden pallet.
A number of alternative pallet constructions have been tried, but none has been successful. For example, pallets have been made entirely of metal. One example of such a metal pallet is described in the specification of West German patent application No P 21 11 135.3. Unfortunately, when that type of pallet is lifted on the metal tynes of a fork-lift, the slats of the pallet tend to slide on the tynes as a result of the lack of friction, with potentially disastrous results.
Other types of nail-free pallet have been described in (i) the specification of my Australian patent application No. 32537/84, (ii) the specification of West German patent No 912317, and (iii) the specification of my International patent application No PCT/AU89/00017 (WIPO publication No 89/06625). Those pallets, however, are either not strong enough to withstand the structural stresses to which pallets are subjected in normal use, or they are too expensive to manufacture to be commercially viable.